1. Field of the Invention
The present invention relates to a curved pipe manufacturing method and an apparatus for carrying out the same in which a straight pipe of a stainless steel or the like is pressed into a fixed die having a curved cavity of a circular arc to form a curved pipe.
2. Description of the Prior Art
U.S. Pat. No. 4,759,206 discloses a curved pipe manufacturing method employing an apparatus as illustrated in FIG. 6, invented by the inventor of the present invention. According to this known curved pipe manufacturing method and apparatus, a work, namely, a straight pipe 65, is pressed with a presser rod 69 into a curved space, which conforms to the shape of a curved pipe to be formed and is defined by a curved cavity 64 formed in a fixed die 61 so as to extend from the entrance opening 62 to the exit opening 63 of the fixed die 61, and a curved mandrel 67 is secured to a movable block 66 so as to be inserted into and extracted from the curved cavity 64 of the fixed die 61, through the exit opening 63 of the fixed die 61, to form a curved pipe. The movable block 66 is turned to extract only the mandrel 67 from the fixed die 61, and then the movable block 66 is turned further to insert an ejecting rod 68, attached to the movable block 66 opposite to the mandrel 67, into the curved cavity 64 of the fixed die 61, from the entrance opening 62 of the fixed die 61, to thereby push out the curved pipe from the fixed die 61 with the ejecting rod 68, characterized in that, in the middle of pressing the work into the curved space by the pressure rod from the entrance opening 62, the action of presser rod 69 is interrupted in pressing the work 65 into the curved space and the mandrel 67 is removed slightly from a curved portion of the work 65 and then the advancement of the presser rod 69 is restarted to press the work 65 further into the curved space to complete the curved pipe.
However, according to the known method and apparatus, inasmuch as in the middle of manufacturing the curved pipe, there comprises the steps of interrupting the action of presser rod in pressing the work into the curved space and slightly removing the mandrel from a curved portion of the work and then restarting the advancement of the presser rod to press the work further into the curved space to complete the curved pipe, there arises problems that the curved pipe accompanies the mandrel 7 during its removal e.g., the curved pipe is extracted from the exit opening 3 together with the mandrel 7 as well as this process for manufacturing a curved pipe is complicated and the apparatus for carrying out the same is also complicated.